Approaches to provide dynamic input in Java
- BufferedReader Class with InputStreamReader Class
- Scanner Class
- Console class
- Command Line Arguments
BufferedReader Class with InputStreamReader Class
BufferedReader Class with InputStreamReader Class
The BufferedReader and InputStreamReader classes are essential in Java for handling input from various sources, such as the command line, files, or network streams. When used together, they provide an efficient way to read text-based input while optimizing performance.
Problem: Command-line Input for a User Profile
We will create a program that:
- Reads user inputs (name, age, and email).
- Validates the inputs (for example, age must be a number and email must contain "@" and ".").
- Displays the user's profile if the input is valid.
Code Example
x
import java.io.*;public class UserProfile { public static void main(String[] args) { BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); try { // Input and validation for name System.out.print("Enter your name: "); String name = br.readLine(); if (name.isEmpty()) { System.out.println("Name cannot be empty!"); return; } // Input and validation for age System.out.print("Enter your age: "); String ageInput = br.readLine(); int age = 0; try { age = Integer.parseInt(ageInput); if (age <= 0) { System.out.println("Age must be a positive number."); return; } } catch (NumberFormatException e) { System.out.println("Invalid age. Please enter a valid number."); return; } // Input and validation for email System.out.print("Enter your email: "); String email = br.readLine(); if (!isValidEmail(email)) { System.out.println("Invalid email format. Please enter a valid email."); return; } // Display the user profile System.out.println("\nUser Profile:"); System.out.println("Name: " + name); System.out.println("Age: " + age); System.out.println("Email: " + email); } catch (IOException e) { System.out.println("Error reading input: " + e.getMessage()); } } // Helper method to validate email public static boolean isValidEmail(String email) { // Simple email validation logic: check for '@' and '.' return email.contains("@") && email.contains("."); }}Output
Scenario 1: Valid Input
Enter your name: Alice
Enter your age: 25
Enter your email: alice@example.com
User Profile:
Name: Alice
Age: 25
Email: alice@example.comExplanation:
- BufferedReader and InputStreamReader:
- We use
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));to chain these two classes, allowing for efficient and easy reading of character input from the console. System.inis theInputStreamconnected to the console, andInputStreamReaderconverts this byte-based stream into character-based data.BufferedReaderadds efficiency with its buffer and provides thereadLine()method to read whole lines of input.
- We use
- Input and Validation:
- The program first asks the user for their name. If the input is empty, the program displays an error and exits.
- Then, the user is prompted for their age, which must be a valid number. If it's not, a
NumberFormatExceptionis caught, and the user is informed that the input is invalid. - Finally, the email input is validated by checking whether it contains both an "@" and a "." using the
isValidEmail()helper function.
- Displaying Profile:
- Once all inputs are validated, the program displays the user profile: name, age, and email.
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